What causes cataracts?
The lens is made of mostly water and protein. The protein is arranged in a specific way that keeps the lens clear and allows light to pass through it to focus a clear image onto the retinal surface. As we age, some of the protein may clump together and start to cloud a small area of the lens. This is our understanding of the cause of an age-related cataract. Over time, the cataract may become denser or cloud more area of the lens, making it more difficult to see through. A cataract is not a growth or tumor.
There are many other causes of cataracts beyond advancing age. Whatever the cause, all cataracts are a result of similar changes to the protein of the lens, similarly resulting in visual blurring or visual loss.
Blunt or penetrating injury to the eye may result in a cataract, either immediately after the injury or some weeks to years afterward. A cataract following an injury may appear and then not increase in density (be stationary) or be progressive. Eye surgery for other conditions can also cause cataracts. Excessive exposure to ionizing radiation (X-ray), infrared radiation (as in glass blowers), or ultraviolet radiation may also cause cataracts.
Diabetes is associated with the development of cataracts. Inflammatory disease of the eye, such as iritis or uveitis, may cause or accelerate the development of cataract in the involved eye.
There are many genetic illnesses that are associated with the development of cataracts. These include myotonic dystrophy, galactosemia, homocystinuria, Wilson's disease and Down syndrome, plus many others. Congenital infections with herpes simplex, rubella, toxoplasmosis, syphilis, and cytomegalic inclusion disease may also result in cataracts.
There are many medications which, when taken over a long period of time, can cause secondary cataracts. The most common of these are oral corticosteroids, such as prednisone, which currently are used for a wide variety of medical conditions.
The term "congenital cataract" is used when a baby is born with any clouding of the lens. This may be present in one or both eyes, be stationary or be progressive. Causes include genetic disorders or infectious or non-infectious intrauterine developmental disorders, both often associated with other physical abnormalities of the baby.
Atopic dermatitis, other diseases of the skin and mucous membranes, hypothyroidism, and hyperparathyroidism are associated with the early development of cataracts.
Patients who develop cataracts in both eyes at an early age often have family members who have also developed cataracts prematurely, implying a genetic cause, even in the absence of a recognized underlying disease.